Cutting tool

ABSTRACT

A cutting tool includes: a substrate; and a coating film disposed on the substrate, wherein the coating film includes an α-Al 2 O 3  layer, the α-Al 2 O 3  layer includes a plurality of α-Al 2 O 3  crystal grains, and has a TC(006) of more than 5 in texture coefficient TC(hkl), and a hardness H1 of the α-Al 2 O 3  layer at a room temperature and a hardness H2 of the α-Al 2 O 3  layer at 800° C. represent a relation of the following expression A-1: 
       0&lt;{(H1−H2)/H1}×100&lt;60   Expression A-1.

TECHNICAL FIELD

The present disclosure relates to a cutting tool.

BACKGROUND ART

A cutting tool having a coating film formed on a substrate hasconventionally been used. Recently, techniques have been proposed forenhancing the performance of the cutting tool, such as a technique forimproving the quality of the coating film by changing thecrystallographic texture of Al₂O₃. For example, Japanese PatentLaying-Open No. 2008-246664 (PTL 1) proposes a cutting tool including anα-Al₂O₃ layer having a (006) texture on a substrate composed of acemented carbide.

CITATION LIST Patent Literature

PTL 1: Japanese Patent Laying-Open No. 2008-246664

SUMMARY OF INVENTION

A cutting tool of the present disclosure is a cutting tool including:

-   -   a substrate; and    -   a coating film disposed on the substrate, wherein    -   the coating film includes an α-Al₂O₃ layer,    -   the α-Al₂O₃ layer includes a plurality of α-Al₂O₃ crystal        grains, and has a TC(006) of more than 5 in texture coefficient        TC(hkl), and    -   a hardness H1 of the α-Al₂O₃ layer at a room temperature and a        hardness H2 of the α-Al₂O₃ layer at 800° C. represent a relation        of the following expression A-1:

0<{(H1−H2)/H1}×100<60   Expression A-1.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram illustrating a representative exemplaryconfiguration of a cutting tool according to a first embodiment.

FIG. 2 is a diagram illustrating another exemplary configuration of thecutting tool according to the first embodiment.

FIG. 3 is a diagram illustrating another exemplary configuration of thecutting tool according to the first embodiment.

FIG. 4 is a diagram illustrating another exemplary configuration of thecutting tool according to the first embodiment.

FIG. 5 is a diagram illustrating a plastic deformation amount.

FIG. 6 is a diagram illustrating the plastic deformation amount.

DETAILED DESCRIPTION Problem to be Solved by the Present Disclosure

In recent years, a cutting tool having a long tool life has beenrequired even in a more efficient cutting process. Particularly, a toolhaving a long tool life has been required even in high-speedhigh-feeding processing of high-carbon chromium steel.

Thus, the present disclosure has an object to provide a tool having along tool life particularly even in high-speed high-feeding processingof high-carbon chromium steel.

Advantageous Effect of the Present Disclosure

The cutting tool of the present disclosure can have a long tool lifeparticularly even in high-speed high-feeding processing of high-carbonchromium steel.

Description of Embodiments

First, embodiments of the present disclosure are listed and described.

(1) A cutting tool of the present disclosure is a cutting toolincluding:

a substrate; and

a coating film disposed on the substrate, wherein

the coating film includes an α-Al₂O₃ layer,

the α-Al₂O₃ layer includes a plurality of α-Al₂O₃ crystal grains, andhas a TC(006) of more than 5 in texture coefficient TC(hkl), and

a hardness H1 of the α-Al₂O₃ layer at a room temperature and a hardnessH2 of the α-Al₂O₃ layer at 800° C. represent a relation of the followingexpression A-1:

0<{(H1−H2)/H1}×100<60   Expression A-1.

-   -   The cutting tool of the present disclosure can have a long tool        life particularly even in the high-speed high-feeding processing        of high-carbon chromium steel.

(2) The hardness H1 and the hardness H2 preferably represent a relationof the following expression A-2:

0<{(H1−H2)/H1}×100<55   Expression A-2.

This leads to a further improved tool life of the cutting tool.

(3) The TC(006) is preferably more than 5 and 8 or less. Thus, the wearresistance of the cutting tool is improved, thereby further improvingthe tool life.

(4) The TC(006) is preferably more than 6 and 8 or less. Thus, the wearresistance of the cutting tool is improved, thereby further improvingthe tool life.

(5) An elastic modulus E1 of the α-Al₂O₃ layer at the room temperatureand an elastic modulus E2 of the α-Al₂O₃ layer at 800° C. preferablyrepresent a relation of the following expression B-1:

0<{(E1−E2)/E1}×100<10   Expression B-1.

Thus, the breakage resistance of the cutting tool at a high temperatureis improved, thereby further improving the tool life of the cuttingtool.

(6) A plastic deformation amount hp of the α-Al₂O₃ layer at 800° C. ispreferably 0 nm or more and 100 nm or less.

Thus, the plastic deformation resistance of the cutting tool at a hightemperature is improved, thereby further improving the tool life of thecutting tool.

(7) An average film thickness of the α-Al₂O₃ layer is preferably 2 μm ormore and 15 μm or less. This leads to a further improved tool life ofthe cutting tool.

Details of Embodiments of the Present Disclosure

A specific example of a cutting tool of the present disclosure will bedescribed below with reference to figures. The same reference charactersindicate the same or equivalent portions in the figures of the presentdisclosure. Further, a relation of such a dimension as a length, awidth, a thickness, or a depth is modified as appropriate for clarityand brevity of the figures and does not necessarily represent an actualdimensional relation.

In the present specification, the expression “A to B” represents a rangeof lower to upper limits (i.e., A or more and B or less), When no unitis indicated for A and a unit is indicated only for B, the unit of A isthe same as the unit of B.

When a compound or the like is expressed by a chemical formula in thepresent specification and an atomic ratio is not particularly limited,it is assumed that all the conventionally known atomic ratios areincluded. The atomic ratio should not be necessarily limited only to onein the stoichiometric range. For example, when “TiCN” is described, theatomic ratio of the TiCN includes all the conventionally known atomicratios. Moreover, in the present embodiment, a metal element such as Tior Al and a non-metal element such as N (nitrogen), O (oxygen), or C(carbon) does not need to necessarily constitute a stoichiometriccomposition.

First Embodiment: Cutting Tool

A cutting tool of the present disclosure is a cutting tool including: asubstrate; and a coating film disposed on the substrate, wherein thecoating film includes an α-Al₂O₃ layer, the α-Al₂O₃ layer includes aplurality of α-Al₂O₃ crystal grains, and has a TC(006) of more than 5 intexture coefficient TC(hkl), and a hardness H1 of the α-Al₂O₃ layer at aroom temperature and a hardness H2 of the α-Al₂O₃ layer at 800° C.represent a relation of the following expression A-1:

0<{(H1−H2)/H1}×100<60   Expression A-1.

The cutting tool of the present disclosure can have a long tool lifeparticularly even in the high-speed high-feeding processing ofhigh-carbon chromium steel. A reason for this is unknown, but ispresumed as described in (i) and (ii) below.

(i) In the cutting tool of the present disclosure, the value of theTC(006) of the α-Al₂O₃ layer is more than 5. Accordingly, fine filmchipping and wear are less likely to occur in the α-Al₂O₃ layer, and theα-Al₂O₃ layer can have excellent wear resistance particularly even undera high temperature condition of the high-speed high-feeding processingof high-carbon chromium steel. Thus, the cutting tool can have a longtool life. It should be noted that details of the TC(006) of the α-Al₂O₃layer will be described later.

(ii) in the cutting tool of the present disclosure, hardness H1(hereinafter, also referred to as “room temperature hardness H1”) of theα-Al₂O₃ layer at the room temperature and hardness H2 (hereinafter, alsoreferred to as “high temperature hardness H2”) of the α-Al₂O₃ layer at800° C. represent the relation of the following expression A-1:

0<{(H1−H2)/H1}×100<60   Expression A-1.

Expression A-1 indicates that a ratio of decrease of high temperaturehardness H2 of the α-Al₂O₃ layer with respect to room temperaturehardness H1 is less than 60%. That is, it is indicated that when roomtemperature hardness H1 and high temperature hardness H2 of the α-Al₂O₃layer satisfy expression A-1, the α-Al₂O₃ layer maintains a highhardness even at a high temperature. Therefore, the cutting tool havingthe α-Al₂O₃ layer can have excellent wear resistance and long tool lifeparticularly even under the high temperature condition of the high-speedhigh-feeding processing of high-carbon chromium steel.

It should be noted that in the current technology, the morphology of theα-Al₂O₃ layer at 800° C. cannot be analyzed to define its structure.Therefore, as a result of diligent study, the present inventors definedthe present disclosure by defining the relation between room temperaturehardness H1. and high temperature hardness H2 of the α-Al₂O₃ layer.

Configuration of Cutting Tool

As shown in FIG. 1 , a cutting tool 1 of the present embodimentincludes: a substrate 10; and a coating film 15 disposed on substrate10, wherein coating film 15 includes an α-Al₂O₃ layer 11. Coating film15 preferably coats the entire surface of the substrate. However, acoating film that does not coat a portion of the substrate and a coatingfilm having a partially different configuration are not deviated fromthe scope of the present disclosure.

Coating film 15 may include other layer(s) in addition to α-Al₂O₃ layer11. For example, as shown in FIG. 2 , a coating film 25 may furtherinclude an underlying layer 12 disposed between substrate 10 and α-Al₂O₃layer 11.

As shown in FIG. 3 , a coating film 35 may further include a surfacelayer 13 disposed on α-Al₂O₃ layer 11.

As shown in FIG. 4 , a coating film 45 may further include anintermediate layer 14 disposed between underlying layer 12 and α-Al₂O₃layer 11.

Application of Cutting Tool

Examples of the cutting tool of the present disclosure include a drill,an end mill (for example, a ball end mill), an indexable cutting insertfor drill, an indexable cutting insert for end mill, an indexablecutting insert for milling, an indexable cutting insert for turning, ametal saw, a gear cutting tool, a reamer, a tap, and the like.

Coating Film

The coating film includes the α-Al₂O₃ layer. For example, the coatingfilm can be constituted of a plurality of layers that include one ormore α-Al₂O₃ layers and that further includes the other layer(s).

Examples of the other layer(s) include the underlying layer, the surfacelayer, the intermediate layer, and the like. More specifically, theexamples of the other layer(s) include a TiCNO layer or a TiBN layer, aTiC layer, a TiN layer, a TiAlN layer, a TiSiN layer, an AlCrN layer, aTiAlSiN layer, a TiAlNO layer, an AlCrSiCN layer, a TiCN layer, a TiSiClayer, a CrSiN layer, an AlTiSiCO layer, a TiSiCN layer, and the like.

The average thickness of the coating film is preferably 3 to 35 μm.Thus, the coating film can have excellent wear resistance and detachmentresistance. The average thickness of the coating film is more preferably5 to 20 μm.

The thickness of the coating film is measured, for example, by obtaininga cross sectional sample parallel to the normal direction of the surfaceof the substrate and by observing the sample using a scanningtransmission electron microscope (STEM). Examples of the scanningtransmission electron microscope include JEM-2100F (trademark) providedby JEOL.

In the present specification, the term “thickness” refers to an averagethickness. Specifically, an observation magnification for the crosssectional sample is set to 5000× to 10000×, an observation area is setto 100 to 500 μm², thicknesses at 10 positions in one visual field aremeasured, and the average value of the thicknesses is defined as the“thickness”. The thickness and average thickness of each ofbelow-described layers are also measured and calculated in the samemanner.

α-Al₂O₃ Layer Configuration of α-Al₂O₃ Layer

In the present disclosure, the α-Al₂O₃ layer is a layer including aplurality of α-Al₂O₃ (aluminum oxide having an a type crystal structure)crystal grains. That is, the α-Al₂O₃ layer is constituted ofpolycrystalline α-Al₂O₃. The average grain size of the α-Al₂O₃ crystalgrains is preferably 100 to 2000 nm.

TC(006)

In the present disclosure, the α-Al₂O₃ layer has a TC(006) of more than5 in texture coefficient TC(hkl) represented by the following expression(1):

$\begin{matrix}{{T{C({hkl})}} = {\frac{I({hkl})}{I_{0}\left( {hkl} \right)}\left\{ {\frac{1}{n}{\sum_{1}^{n}\frac{I\left( {hkl} \right)}{I_{0}({hkl})}}} \right\}^{- 1}}} & (1)\end{matrix}$

In the expression (1), I(hkl) represents an x-ray diffraction intensityof a (hkl) reflection plane, and I₀(hkl) represents a standard intensityaccording to PDF card No. 00-010-0173 of the ICDD. In the expression(1), n represents the number of reflections used for the calculation andis eight in the present embodiment. (hkl) planes used for reflection are(012), (104), (110), (006), (113), (024), (116), and (300).

ICDD (registered trademark) is an abbreviation for International Centrefor Diffraction Data. PDF (registered trademark) is an abbreviation forPowder Diffraction File.

The TC(006) of the α-Al₂O₃ layer in the present embodiment can beexpressed by the following expression (2).

$\begin{matrix}{{{TC}(006)} = {\frac{I\left( {006} \right)}{I_{o}\left( {006} \right)}\left\{ {\frac{1}{8}{\sum_{1}^{8}\frac{I\left( {hkl} \right)}{I_{o}({hkl})}}} \right\}^{- 1}}} & (2)\end{matrix}$

Therefore, “TC(006) of more than 5 in texture coefficient TC(hkl)” meansthat a numerical value given by the above expression (2) which isdetermined by substituting TC(006) in the expression (1) is more than 5.In the α-Al₂O₃ layer in which the value of TC(006) is more than 5, finefilm chipping and wear are less likely to occur, and the α-Al₂O₃ layercan have excellent wear resistance particularly even under the hightemperature condition of the high-speed high-feeding processing ofhigh-carbon chromium steel. Therefore, the cutting tool can have a longtool life.

The value of TC(006) is preferably more than 6 and more preferably morethan 7. A greater value of TC(006) enables effective improvement of thewear resistance.

While the upper limit of the value of TC(006) is not limited, the upperlimit may be 8 or less since the number of reflection planes used forthe calculation is 8. The value of TC(006) can be more than 5 and 8 orless, more than 6 and 8 or less, or more than 7 and 8 or less.

This TC(hkl) can be measured through an analysis by means of an x-raydiffractometer. TC(hkl) can for example be measured by means of SmartLab(registered trademark) manufactured by Rigaku Corporation (scanningspeed: 21.7°/min, step: 0.01°, scanning range: 15 to 140°) under thefollowing conditions. It should be noted that the result of measurementof the TC(hkl) by means of the x-ray diffractometer is herein referredto as “XRD result.”

Characteristic x-ray: Cu-Kα

tube voltage: 45 kV

tube current: 200 mA

filter: multilayer mirror

optical system: focusing method

x-ray diffraction method: θ-2θ method

When using the x-ray diffractometer, x rays are applied to the rake faceof the cutting tool. Usually the rake face is formed to be uneven whilethe flank face is flat, and therefore, in order to eliminate disturbancefactors, the x rays are preferably applied to the flank face.Particularly, x rays are applied to portions of the flank face in arange of about 2 to 4 mm from the cutting edge ridgeline portion.Accordingly, reproducibility of the result becomes high.

Hardness

In the present disclosure, hardness H1 of the α-Al₂O₃ layer at the roomtemperature and hardness H2 of the α-Al₂O₃ layer at 800° C. representthe relation of the following expression A-1:

0<{(H1−H2)/H1}×100<60   Expression A-1.

Expression A-1 indicates that the ratio of decrease of high temperaturehardness H2 of the α-Al₂O₃ layer with respect to room temperaturehardness H1 is less than 60%. That is, when room temperature hardness H1and high temperature hardness H2 of the α-Al₂O₃ layer satisfy expressionA-1, the α-Al₂O₃ layer maintains a high hardness even at a hightemperature. Therefore, the cutting tool having the α-Al₂O₃ layer canhave excellent wear resistance and long tool life particularly evenunder the high temperature condition of the high-speed high-feedingprocessing of high-carbon chromium steel.

Room temperature hardness H1 and high temperature hardness H2 preferablyrepresent a relation of the following expression A-2:

0<{(H1−H2)/H1}×100<55   Expression A-2.

The lower limit of room temperature hardness H1 of the α-Al₂O₃ layer canbe 28 GPa or more, 30 GPa or more, or 32 GPa or more. The upper limit ofroom temperature hardness H1 is not particularly limited, but can be,for example, 42 GPa or less, 40 GPa or less, or 38 GPa or less. Roomtemperature hardness H1 can be 28 GPa or more and 42 GPa or less, 30 GPaor more and 42 GPa or less, or 32 GPa or more and 40 GPa or less.

The lower limit of high temperature hardness H2 of the α-Al₂O₃ layer canbe 11 GPa or more, 13 GPa or more, or 15 GPa or more. The upper limit ofhigh temperature hardness H2 is not particularly limited, but can be,for example, 25 GPa or less, 23 GPa or less, or 21 GPa or less. Hightemperature hardness H2 can be 11 GPa or more and 25 GPa or less, 13 GPaor more and 23 GPa or less, or 15 GPa or more and 21 GPa or less.

A method of measuring each of room temperature hardness H1 and hightemperature hardness H2 of the α-Al₂O₃ layer is as follows. First,mirror surface processing is performed onto an arbitrary surface of thetool by cross section polisher processing (CP processing). When thecoating film includes a layer (for example, surface layer) other thanthe α-Al₂O₃ layer on the surface side with respect to the α-Al₂O₃ layer,the mirror surface processing is performed until the α-Al₂O₃ layer isexposed. The processed surface is subjected to high temperaturenanoindenter measurement (indentation test using the apparatus “TI980”provided by Hysitron).

Room temperature hardness H1 is measured by performing the indentationtest onto the tool at the room temperature (25±5° C.). High temperaturehardness H2 is measured by heating a measurement chamber of themeasurement apparatus to 800° C. in an argon (Ar) atmosphere and byperforming the indentation test onto the tool in the atmosphere. In theindentation test, pressing is performed at a load of 8 mN for 2 seconds,holding is performed for 1 second in the pressed state, and the load isunloaded in 2 seconds. The indentation test is performed at 10 positionson the surface of the tool. In the present specification, the averagevalue of the room temperature hardnesses at the 10 positions is definedas room temperature hardness H1 of the α-Al₂O₃ layer. Likewise, theaverage value of the high temperature hardnesses at the 10 positions isdefined as high temperature hardness H2 of the α-Al₂O₃ layer.

Elastic Modulus

In the present disclosure, elastic modulus E1 (hereinafter, alsoreferred to as “room temperature elastic modulus E1 ”) of the α-Al₂O₃layer at the room temperature and elastic modulus E2 (hereinafter, alsoreferred to as “high temperature elastic modulus”) of the α-Al₂O₃ layerat 800° C. preferably represent a relation of the following expressionB-1:

0<{(E1−E2)/E1}×100<10   Expression B-1.

Expression B-1 indicates that a ratio of decrease of high temperatureelastic modulus E2 of the α-Al₂O₃ layer with respect to room temperatureelastic modulus E1 is less than 10%. That is, it is indicated that whenroom temperature elastic modulus E1 and high temperature elastic modulusE2 of the α-Al₂O₃ layer satisfy expression B-1, the α-Al₂O₃ layermaintains a high elastic modulus even at a high temperature. Therefore,the cutting tool having the α-Al₂O₃ layer can have excellent breakageresistance and long tool life particularly even under the hightemperature condition of the high-speed high-feeding processing ofhigh-carbon chromium steel.

Room temperature elastic modulus E1 and high temperature elastic modulusE2 preferably represent a relation of the following expression B-2:

0<{(E1−E2)/E1}×100<8   Expression B-2.

The lower limit of room temperature modulus E1 of the α-Al₂O₃ layer canbe 300 GPa or more, 315 GPa or more, or 325 GPa or more. The upper limitof room temperature elastic modulus E1 is not particularly limited, butcan be 400 GPa or less, 380 GPa or less, or 350 GPa or less, forexample. Room temperature elastic modulus E1 can be 300 GPa or more and400 GPa or less, 315 GPa or more and 380 GPa or less, or 325 GPa or moreand 350 GPa or less.

The lower limit of high temperature elastic modulus E2 of the α-Al₂O₃layer can be 280 GPa or more, 290 GPa or more, or 300 GPa or more. Theupper limit of high temperature elastic modulus E2 is not particularlylimited, but can be, for example, 350 GPa or less, 340 GPa or less, or330 GPa or less. High temperature elastic modulus E2 can be 280 GPa ormore and 350 GPa or less, 290 GPa or more and 340 GPa or less, or 300GPa or more and 330 GPa or less.

Room temperature modulus E1 and high temperature modulus E2 of theα-Al₂O₃ layer can be measured using the same apparatus and conditions asthose for room temperature hardness H1 and high temperature hardness H2of the α-Al₂O₃ layer. Specifically, mirror processing is performed ontoan arbitrary surface of the tool by cross section polisher processing(CP processing), and the processed surface is subjected to hightemperature nanoindenter measurement (indentation test using theapparatus “TI980” provided by Hysitron).

Room temperature modulus E1 is measured by performing the indentationtest onto the tool at the room temperature (25±5° C.). High temperatureelastic modulus E2 is measured by heating a measurement chamber of themeasurement apparatus to 800° C. in an argon (Ar) atmosphere and byperforming the indentation test onto the tool in the atmosphere. In theindentation test, pressing is performed at a load of 8 mN for 2 seconds,holding is performed for 1 second in the pressed state, and the load isunloaded in 2 seconds. The indentation test is performed at 10 positionson the surface of the tool. In the present specification, the averagevalue of the room temperature elastic moduli at the 10 positions isdefined as room temperature elastic modulus E1 of the α-Al₂O₃ layer.Likewise, the average value of the high temperature elastic moduli atthe 10 positions is defined as high temperature elastic modulus E2 ofthe α-Al₂O₃ layer.

Plastic Deformation Amount

In the present disclosure, a plastic deformation amount hp (hereinafter,also referred to as “high temperature plastic deformation amount hp”) ofthe α-Al₂O₃ layer at 800° C. is preferably 0 mn or more and 100 nm orless. Thus, the plastic deformation resistance of the cutting tool at ahigh temperature is improved, thereby further improving the tool life ofthe cutting tool.

The upper limit of high temperature plastic deformation amount hp of theα-Al₂O₃ layer can be 100 nm or less, 99 nm or less, or 98 nm or less.The lower limit of high temperature plastic deformation amount hp is notparticularly limited, and can be 0 nm or more. High temperature plasticdeformation amount hp can be 0 nm or more and 100 nm or less, 0 nm ormore and 99 nm or less, or 0 nm or more and 98 nm or less.

The plastic deformation amount in the present specification will bedescribed with reference to FIGS. 5 and 6 . As shown in FIG. 5 , theplastic deformation amount is defined as an amount of deformation of asample 7 when an apex of an indenter 8 having a triangular pyramid shapeis pressed onto the sample and then it is unloaded. In FIG. 6 , thesurface of the sample before being pressed by the indenter is indicatedby a solid line 7 a, the surface of the sample pressed by the indenteris indicated by a broken line 7 b, and the surface of the sample afterthe unloading of the indenter is indicated by a solid line 7 c. Amaximum value hp of a difference in the depth direction between thesurface of the sample before being pressed by the indenter (solid line 7a) and the surface of the sample after the unloading of the indenter(solid line 7 c) corresponds to the plastic deformation amount.

Plastic deformation amount hp of the α-Al₂O₃ layer at 800° C. can bemeasured using the same apparatus and conditions as those for hightemperature hardness H2 of the α-Al₂O₃ layer. Specifically, mirrorprocessing is performed onto an arbitrary surface of the tool by crosssection polisher processing (CP processing), and the processed surfaceis subjected to high temperature nanoindenter measurement (with theapparatus “TI980” provided by Hysitron).

Plastic deformation amount hp at 800° C. is measured by heating ameasurement chamber of the measurement apparatus to 800° C. in an argon(Ar) atmosphere and by performing the indentation test onto the tool inthe atmosphere. In the indentation test, pressing is performed at a loadof 8 mN for 2 seconds, holding is performed for 1 second in the pressedstate, and the load is unloaded in 2 seconds. The indentation test isperformed at 10 positions on the surface of the tool. In the presentspecification, the average value of the plastic deformation amounts atthe 10 positions is defined as plastic deformation amount hp of theα-Al₂O₃ layer at 800° C.

Thickness

The average thickness of the α-Al₂O₃ layer is preferably 2 μm or moreand 15 μm or less. Thus, both wear resistance and chipping resistancecan be attained. The lower limit of the average thickness of the α-Al₂O₃layer can be 2 μm or more, 3.5 μm or more, or 5 μm or more. The upperlimit of the average thickness of the α-Al₂O₃ layer can be 15 μm orless, 13 μm or less, or 11 μm or less. The average thickness of theα-Al₂O₃ layer can be 2 μm or more and 15 μm or less, 3.5 μm or more and13 μm or less, or 5 μm or more and 11 μm or less.

The thickness of the α-Al₂O₃ layer can be confirmed by observing thecross sectional sample of the cutting tool using the scanningtransmission electron microscope (STEM) or the like as described above.

Other Layer(s)

As described above, the coating film can include the other layer(s) inaddition to the α-Al₂O₃ layer. As shown in FIGS. 2 to 4 , examples ofthe other layer(s) include underlying layer 12, surface layer 13,intermediate layer 14, and the like.

Underlying Layer

The underlying layer is disposed between the substrate and the α-Al₂O₃layer. The underlying layer can be, for example, a TiN layer. The TiNlayer preferably has an average thickness of 0.1 μm or more and 20 μm orless. Thus, the coating film can have excellent wear resistance andbreakage resistance.

Surface Layer

Preferably, any one of Ti (titanium) carbide, Ti nitride and Ti borideis a main component of the surface layer, for example. The surface layeris a layer disposed closest to the surface side in the coating film. Itshould be noted, however, that the surface layer may not be formed atthe cutting edge ridgeline portion. For example, when the other layer(s)are not formed on the α-Al₂O₃ layer, the surface layer is disposeddirectly on the α-Al₂O₃ layer.

The expression “any one of Ti carbide, Ti nitride, and Ti boride is amain component” means that 90 mass % or more of any one of Ti carbide,Ti nitride, and Ti boride is included. It means that the surface layerpreferably consists of any one of Ti carbide, Ti nitride, and Ti boride,besides inevitable impurities.

Among the Ti carbide, the Ti nitride, and the Ti carbonitride, the Tinitride (namely the compound expressed as TiN) is particularlypreferable for use as the main component of the surface layer. Amongthese compounds, TiN assumes the most distinct color (assumes gold) andtherefore has an advantage of making it easy to identify a corner(identify a used part) of a cutting insert after used for cutting. Thesurface layer preferably consists of a TiN layer.

The surface layer preferably has an average thickness of 0.05 μm or moreand 1 μm or less. This leads to improved adhesion between the surfacelayer and an adjacent layer. The upper limit of the average thickness ofthe surface layer can be 0.8 μm or less or 0.6 μm or less. The lowerlimit of the average thickness can be 0.1 μm or more or 0.2 μm or more.

Intermediate Layer

The intermediate layer is disposed between the underlying layer and theα-Al₂O₃ layer. The intermediate layer can be, for example, a TiCN layer.Since the TiCN layer is excellent in wear resistance, the coating filmcan be provided with more suitable wear resistance. The intermediatelayer preferably has an average thickness of 1 μm or more and 20 μm orless.

Second Embodiment: Method of Manufacturing Cutting Tool

The cutting tool of the first embodiment can be manufactured by formingthe coating film on the substrate by a chemical vapor deposition (CVD)method. When the other layer(s) than the α-Al₂O₃ layer are formed in thecoating film, the other layer(s) can be formed under conventionallyknown conditions using a chemical vapor deposition apparatus. On theother hand, the α-Al₂O₃ layer can be formed, for example, as describedbelow. It should be noted that the cutting tool of the first embodimentis not limited to the one manufactured by the following manufacturingmethod, and may be manufactured by another manufacturing method.

For a source gas, AlCl₃, HCl, CO₂, H₂S, N₂, Ar, and H₂ are used.Blending amounts in the source gas are changed between a period of timein 30 minutes from the start of film formation (hereinafter, alsoreferred to as “first half period”) and a subsequent period of timeafter 30 minutes from the start of film formation (hereinafter, alsoreferred to as “second half period”). Specifically, the blending amountsin the first half period are as follows: 1 to 6 volume % of AlCl₃; 5 to10 volume % of HCl; 0.5 to 4 volume % of CO₂; 1 to 4 volume % of H₂S; 1to 10 volume % of N₂; 0.1 to 10 volume % of Ar; and a remainder of H₂.The blending amounts in the second half period are the same as theblending amounts in the first half period except that the blendingamount of HCl is smaller than that in the first half period and is 2 to8 volume % and the amount of H₂ is changed accordingly. That is, thecontent of HCl in the source gas in the second half period is madesmaller than that in the first half period.

By thus changing the blending amount of HCl in the source gas betweenthe first half period and the second half period (specifically, bycausing the amount of HCl in the second half period to be smaller thanthat in the first half period), the α-Al₂O₃ layer of the presentembodiment having high hardness even at a high temperature can beformed. This is newly found by the present inventors.

Film formation conditions for the α-Al₂O₃ layer can be, for example, asfollows: a temperature is 950 to 1050° C., a pressure is 1 to 5 kPa, anda gas flow rate (total amount of gases) is 50 to 100 L/min. The sourcegas can be introduced into the reaction container at an introductionrate of 1.7 to 3.5 m/sec.

Clause 1

In the cutting tool of the present disclosure, the TC(006) of theα-Al₂O₃ layer is preferably more than 7 and 8 or less.

Clause 2

In the cutting tool of the present disclosure, the average thickness ofthe whole of the coating film is preferably 3 μm or more and 35 μm orless.

In the cutting tool of the present disclosure, the average thickness ofthe whole of the coating film is preferably 5 μm or more and 20 μm orless.

Clause 3

In the cutting tool of the present disclosure, room temperature hardnessH1 of the α-Al₂O₃ layer can be 28 GPa or more and 42 GPa or less.

In the cutting tool of the present disclosure, room temperature hardnessH1 of the α-Al₂O₃ layer can be 30 GPa or more and 42 GPa or less.

In the cutting tool of the present disclosure, room temperature hardnessH1 of the α-Al₂O₃ layer can be 32 GPa or more and 40 GPa or less.

Clause 4

In the cutting tool of the present disclosure, high temperature hardnessH2 of the α-Al₂O₃ layer can be 11 GPa or more and 25 GPa or less.

In the cutting tool of the present disclosure, high temperature hardnessH2 of the α-Al₂O₃ layer can be 13 GPa or more and 23 GPa or less.

In the cutting tool of the present disclosure, high temperature hardnessH2 of the α-Al₂O₃ layer can be 15 GPa or more and 21 GPa or less.

Clause 5

In the cutting tool of the present disclosure, room temperature elasticmodulus E1 of the α-Al₂O₃ layer can be 300 GPa or more and 400 GPa orless.

In the cutting tool of the present disclosure, room temperature elasticmodulus E1 of the α-Al₂O₃ layer can be 315 GPa or more and 380 GPa orless.

In the cutting tool of the present disclosure, room temperature elasticmodulus E1 of the α-Al₂O₃ layer can be 325 GPa or more and 350 GPa orless.

Clause 6

In the cutting tool of the present disclosure, high temperature elasticmodulus E2 of the α-Al₂O₃ layer can be 280 GPa or more and 350 GPa orless.

In the cutting tool of the present disclosure, high temperature elasticmodulus E2 of the α-Al₂O₃ layer can be 290 GPa or more and 340 GPa orless.

In the cutting tool of the present disclosure, high temperature elasticmodulus E2 of the α-Al₂O₃ layer can be 300 GPa or more and 330 GPa orless.

Clause 7

In the cutting tool of the present disclosure, high temperature plasticdeformation amount hp of the α-Al₂O₃ layer can be 0 nm or more and 99 nmor less.

In the cutting tool of the present disclosure, high temperature plasticdeformation amount hp of the α-Al₂O₃ layer can be 0 nm or more and 98 nmor less.

Clause 8

In the cutting tool of the present disclosure, the average thickness ofthe α-Al₂O₃ layer can be 2 μm or more and 15 μm or less.

In the cutting tool of the present disclosure, the average thickness ofthe α-Al₂O₃ layer can be 3.5 μm or more and 13 μm or less.

In the cutting tool of the present disclosure, the average thickness ofthe α-Al₂O₃ layer can be 5 μm or more and 11 μm or less.

Clause 9

In the cutting tool of the present disclosure, the coating filmpreferably includes the underlying layer disposed between the substrateand the α-Al₂O₃ layer.

The underlying layer preferably consists of a TiN layer.

The average thickness of the underlying layer is preferably 0.1 μm ormore and 20 μm or less.

Clause 10

In the cutting tool of the present disclosure, the coating filmpreferably includes the surface layer disposed closest to the surfaceside of the coating film.

The surface layer preferably consists of a TiN layer.

The average thickness of the surface layer is preferably 0.05 μm or moreand 1 μm or less.

Clause 11

In the cutting tool of the present disclosure, the coating filmpreferably includes the intermediate layer disposed between theunderlying layer and the α-Al₂O₃ layer.

The intermediate layer preferably consists of a TiCN layer.

The average thickness of the intermediate layer is preferably 1 μm ormore and 20 μm or less.

EXAMPLES

The following describes the present embodiment more specifically by wayof examples. However, the present embodiment is not limited by theseexamples.

Specimens 1 to 7 Preparation of Substrate

Source material powders having blending compositions shown in Table 1were uniformly mixed, were pressed and shaped into a predeterminedshape, and were then sintered at 1300 to 1500° C. for 1 to 2 hours toobtain a substrate composed of a cemented carbide (model numberCNMG120408N-GU provided by Sumitomo Electric HardMetal).

TABLE 1 Blending Composition (Mass %) Co TiC Cr3C2 NbC TaC WC 5 2 10.31.5 0.5 Remainder

Formation of Coating Film

A coating film was formed on a surface of the substrate obtained asdescribed above, thereby producing a cutting tool. Specifically, thesubstrate is set in a chemical vapor deposition apparatus to form thecoating film on the substrate by the chemical vapor deposition method.The coating film includes a TiN layer (underlying layer), a TiCN layer(intermediate layer), an α-Al₂O₃ layer, and a TiN layer (surface layer).

TiN Layer (Underlying Layer) and TiCN Layer (Intermediate Layer)

The TiN layer (underlying layer) and the TiCN layer (intermediate layer)were formed on the substrate in the above-described order. Filmformation conditions for the TiN layer and the TiCN layer are shown inTable 2.

TABLE 2 Film Formation Conditions Total Amount Source Gas CompositionPressure Temperature of Gases (Volume %) (kPa) (° C.) (L/min) TiN LayerTiCl₄ = 2%, N₂ = 39.7%, 35 910 75 (Underlying H₂ = Remainder Layer) TiCNLayer TiCl₄ = 2%, CH₃CN = 15 840 70 (Intermediate 0.8%, C₂H₄ = 1.3%, H₂= Layer) Remainder TiN Layer TiCl₄ = 0.8%, N₂ = 41%, 80 1000 55 (SurfaceH₂ = Remainder Layer)

For example, for the TiN layer (underlying layer), a source gas having acomposition of 2 volume % of TiCl₄, 39.7 volume % of N₂, and a remainderof H₂ was used. The source gas was supplied to the chemical vapordeposition apparatus to perform the chemical vapor deposition methodunder conditions of a pressure of 35 kPa, a temperature of 910° C., anda flow rate (total amount of gases) of 75 L/min, thereby forming the TiNlayer (underlying layer).

The “remainder” in Table 2 indicates that H₂ occupies the remainder ofthe source gas. The “total amount of gases” indicates a total volumeflow rate introduced into the chemical vapor deposition apparatus perunit time, with a gas in a standard condition (0° C. and 1 atmosphericpressure) being defined as the ideal gas (also applicable to the α-Al₂O₃layer in Table 3). A thickness of each layer was adjusted by adjustingas appropriate a time period for film formation (a rate of filmformation of each layer was approximately from 0.5 to 2.0 μm/hour).

Formation of α-Al₂O₃ Layer

Next, the α-Al₂O₃ layer was formed on the TiCN layer. Film formationconditions for each of the specimens are shown in Table 3. In theformation of the α-Al₂O₃ layer, an introduction rate of the source gaswas set to 2 m/sec, and a gas pipe for jetting the source gas wasrotated at 2 rpm with the substrate being fixed.

TABLE 3 Source Gas Composition (Volume %) Film Formation Conditions HClTotal (After 30 HCl Amount Minutes from (In 30 Minutes of Specimen Startof Film from Start of Pressure Temperature Gases No. AlCl₃ Formation)Film Formation) CO₂ H₂S N₂ Ar H₂ (kPa) (° C.) (L/min) 1 3.8 6.2 8.8 1.52.2 5 1.2 Remainder 4 1000 80 2 2.8 4.2 6.7 0.9 1.4 4 0.9 Remainder 3.51000 70 3 2.2 2.8 6.1 1.2 2.2 4 1.3 Remainder 4 1010 80 4 4.1 5.2 7.31.4 2.5 4.5 0.8 Remainder 3.5 1010 70 5 4.6 5 4 2.5 3.8 5.5 0.4Remainder 4 1000 80 6 3.5 5.5 2.8 2.2 4 3.5 0.7 Remainder 3.5 1000 70 78 3 4.8 2.5 3 4.5 0.7 Remainder 4 1000 80

For example, film formation conditions for specimen 1 are as follows.During a period of time in 30 minutes from the start of film formationof the α-Al₂O₃ layer, a source gas was used which had a composition of3.8 volume % of AlCl₃, 8.8 volume % of HCl, 1.5 volume % of CO₂, 2.2volume % of H₂S, 5 volume % of N₂, 1.2 volume % of Ar, and a remainderof H₂. During a subsequent period of time after 30 minutes from thestart of film formation, a source gas was used which had the samecomposition as described above except that the amount of HCl in thesource gas was set to 6.2 volume % and the amount of the remainder of H₂was changed accordingly. The source gas was supplied to the chemicalvapor deposition apparatus, and the chemical vapor deposition method wasperformed under conditions of a pressure of 4 kPa, a temperature of1000° C., and a flow rate (total amount of gases) of 80 L/min, therebyforming an α-Al₂O₃ layer.

Formation of TIN Layer (Surface Layer)

Next, the TiN layer (surface layer) was formed on the α-Al₂O₃ layer.Film formation conditions are as shown in Table 2.

Configuration of Coating Film

Table 4 shows a configuration of the coating film of each of thespecimens. Regarding Table 4, the composition and thickness of each ofthe coating films were confirmed by a SEM-EDX (scanning electronmicroscope-energy dispersive x-ray spectroscopy).

TABLE 4 Composition of Coatinq Film (μm) Total TiN Layer TiCN Layer TiNLayer Thickness Specimen (Underlying (Intermediate α-Al₂O₃ (Surface ofCoating No. Layer) Layer) Layer Layer) Film (μm) 1 0.5 9.2 6.5 0.5 16.72 0.3 10.4 5.8 0.7 17.2 3 0.8 9.8 6.8 0.6 18 4 0.6 10.1 6.4 0.8 17.9 50.4 9.6 6.2 0.5 16.7 6 0.7 9.8 6 0.7 17.2 7 0.8 10.2 6.4 0.6 18

For example, in the cutting tool of specimen 1, a TiN layer having athickness of 0.5 μm and serving as the underlying layer, a TiCN layerhaving a thickness of 9.2 μm and serving as the intermediate layer, anα-Al₂O₃ layer having a thickness of 6.5 μm, and a TiN layer having athickness of 0.5 μm and serving as the surface layer are formed in theabove-described order on the surface of the substrate as described inTable 1. The total thickness of the coating film of specimen 1 is 16.7μm.

Evaluation on α-Al₂O₃ Layer

In the α-Al₂O₃ layer of each specimen, the TC(006), room temperaturehardness H1, high temperature (800° C.) hardness H2, room temperatureelastic modulus E1, high temperature (800° C.) elastic modulus E2, hightemperature (800° C.) plastic deformation amount hp were measured.Methods of measuring these are as described in the first embodiment, andtherefore will not be described repeatedly.

For example, in specimen 1, H1 was 32.6 GPa, H2 was 15.1 GPa, E1 was 333GPa, and E2 was 310 GPa.

Further, the value of {(H1−H2)/H1}×100 was calculated based on roomtemperature hardness H1 and high temperature hardness H2. The value of{(E1−E2)/E1}×100 was calculated based on room temperature elasticmodulus E1 and high temperature elastic modulus E2. Results are shown inthe columns “TC(006)”, “{(H1−H2)/H1}×100”, “{(E1−E2)/E1}×100 ”, and “hp”in Table 5.

TABLE 5 {(H1 − {(E1 − Specimen H2)H1) × E2)/E1) × hp No. Tc(006) 100 100(nm) 1 5.3 54 7 96 2 5.6 54 6 94 3 6.7 51 7 95 4 6.5 59 7 97 5 5.5 69 899 6 6.6 68 9 98 7 4.3 58 8 98

Cutting Test

Each of the cutting tools obtained above was used to perform a cuttingtest under below-described cutting conditions so as to measure a cuttingtime until a Vb wear amount (flank wear amount) became 0.3 mm. Resultsare shown in Table 6. It is indicated that as the cutting time islonger, the tool life is longer.

Cutting Conditions

Workpiece: SUJ2

Processing: turning for outer diameter of round bar

Cutting rate vc: 400 m/min

Feeding rate f: 0.35 mm/rev

Depth of cut ap: 2.0 mm

Cutting fluid: none

The cutting conditions correspond to the high-speed high-feedingprocessing of high-carbon chromium steel.

TABLE 6 Specimen Tool Life Final No. (min) State 1 20 Wear 2 24 Wear 334 Wear 4 30 Wear 5 6 Wear 6 8 Wear 7 10 Wear

Analysis

Each of the cutting tools of specimens 1 to 4 corresponds to an exampleof the present disclosure. Each of the cutting tools of specimens 5 to 7corresponds to a comparative example. It was confirmed that the toollife in each of specimens 1 to 4 was longer than the tool life in eachof specimens 5 to 7.

Among them, the tool life in each of specimens 2 and 3 was long. This ispresumably due to the following reason: since the value of TC(006) islarge, the wear resistance is further improved.

In each of specimens 5 and 6, the value of {(H1−H2)/H1}×100 is more than60 and decrease in hardness is large to cause progress of wear, thuspresumably resulting in the short tool life.

In specimen 7, the value of TC(006) is 5 or less and the wear resistanceis decreased, thus presumably resulting in the short tool life.

Heretofore, the embodiments and examples of the present disclosure havebeen illustrated, but it has been initially expected to appropriatelycombine the configurations of the embodiments and examples and modifythem in various manners.

The embodiments and examples disclosed herein are illustrative andnon-restrictive in any respect. The scope of the present invention isdefined by the terms of the claims, rather than the embodiments andexamples described above, and is intended to include any modificationswithin the scope and meaning equivalent to the terms of the claims.

REFERENCE SIGNS LIST

1, 21, 31, 41: cutting tool; 7: sample; 7 a, 7 b, 7 c: sample surface;8: indenter; 10: substrate; 11: α-Al₂O₃ layer; 12: underlying layer; 13:surface layer; 14: intermediate layer; 15, 25, 35, 45: coating film

1. A cutting tool comprising: a substrate; and a coating film disposedon the substrate, wherein the coating film includes an α-Al₂O₃ layer,the α-Al₂O₃ layer includes a plurality of α-Al₂O₃ crystal grains, andhas a TC(006) of more than 5 in texture coefficient TC(hkl), and ahardness H1 of the α-Al₂O₃ layer at a room temperature and a hardness H2of the α-Al₂O₃ layer at 800° C. represent a relation of the followingexpression A-1:0<{(H1−H2)/H1}×100<60   Expression A-1.
 2. The cutting tool according toclaim 1, wherein the hardness H1 and the hardness H2 represent arelation of the following expression A-2:0<{(H1−H2)/H1}×100<55   Expression A-2.
 3. The cutting tool according toclaim 1, wherein the TC(006) is more than 5 and 8 or less. 4.-7.(canceled)
 8. The cutting tool according to claim 2, wherein the TC(006)is more than 5 and 8 or less.
 9. The cutting tool according to claim 1,wherein the TC(006) is more than 6 and 8 or less.
 10. The cutting toolaccording to claim 2, wherein the TC(006) is more than 6 and 8 or less.11. The cutting tool according to claim 1, wherein an elastic modulus E1of the α-Al₂O₃ layer at the room temperature and an elastic modulus E2of the α-Al₂O₃ layer at 800° C. represent a relation of the followingexpression B-1:0<{(E1−E2)/E1}×100<10   Expression B-1.
 12. The cutting tool accordingto claim 2, wherein an elastic modulus E1 of the α-Al₂O₃ layer at theroom temperature and an elastic modulus E2 of the α-Al₂O₃ layer at 800°C. represent a relation of the following expression B-1:0<{(E1−E2)/E1}×100<10   Expression B-1.
 13. The cutting tool accordingto claim 10, wherein an elastic modulus E1 of the α-Al₂O₃ layer at theroom temperature and an elastic modulus E2 of the α-Al₂O₃ layer at 800°C. represent a relation of the following expression B-1:0<{(E1−E2)/E1}×100<10   Expression B-1.
 14. The cutting tool accordingto claim 1, wherein a plastic deformation amount hp of the α-Al₂O₃ layerat 800° C. is 0 nm or more and 100 nm or less.
 15. The cutting toolaccording to claim 2, wherein a plastic deformation amount hp of theα-Al₂O₃ layer at 800° C. is 0 nm or more and 100 nm or less.
 16. Thecutting tool according to claim 13, wherein a plastic deformation amounthp of the α-Al₂O₃ layer at 800° C. is 0 nm or more and 100 nm or less.17. The cutting tool according to claim 1, wherein an average thicknessof the α-Al₂O₃ layer is 2 μm or more and 15 μm or less.
 18. The cuttingtool according to claim 2, wherein an average thickness of the α-Al₂O₃layer is 2 μm or more and 15 μm or less.
 19. The cutting tool accordingto claim 8, wherein an average thickness of the α-Al₂O₃ layer is 2 μm ormore and 15 μm or less.
 20. The cutting tool according to claim 10,wherein an average thickness of the α-Al₂O₃ layer is 2 μm or more and 15μm or less.
 21. The cutting tool according to claim 13, wherein anaverage thickness of the α-Al₂O₃ layer is 2 μm or more and 15 μm orless.
 22. The cutting tool according to claim 14, wherein an averagethickness of the α-Al₂O₃ layer is 2 μm or more and 15 μm or less. 23.The cutting tool according to claim 16, wherein an average thickness ofthe α-Al₂O₃ layer is 2 μm or more and 15 μm or less.